// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef MEDIA_BASE_AUDIO_PUSH_FIFO_H_
#define MEDIA_BASE_AUDIO_PUSH_FIFO_H_

#include <memory>

#include "base/callback.h"
#include "base/macros.h"
#include "media/base/audio_bus.h"
#include "media/base/media_export.h"

namespace media {

// Yet another FIFO for audio data that re-buffers audio to a desired buffer
// size.  Unlike AudioFifo and AudioBlockFifo, this FIFO cannot overflow: The
// client is required to provide a callback that is called synchronously during
// a push whenever enough data becomes available.  This implementation
// eliminates redundant memory copies when the input buffer size always matches
// the desired buffer size.
class MEDIA_EXPORT AudioPushFifo final {
public:
    // Called synchronously zero, one, or multiple times during a call to Push()
    // to deliver re-buffered audio.  |frame_delay| refers to the position of the
    // first frame in |output| relative to the first frame in the Push() call.  If
    // negative, this indicates the output contains some data from a prior call to
    // Push().  If zero or positive, the output contains data from the current
    // call to Push().  Clients can use this to adjust timestamps.
    using OutputCallback = base::Callback<void(const AudioBus& output_bus, int frame_delay)>;

    // Creates a new AudioPushFifo which delivers re-buffered audio by running
    // |callback|.
    explicit AudioPushFifo(const OutputCallback& callback);

    ~AudioPushFifo();

    // Returns the number of frames in each AudioBus delivered to the
    // OutputCallback.
    int frames_per_buffer() const { return frames_per_buffer_; }

    // Must be called at least once before the first call to Push().  May be
    // called later (e.g., to support an audio format change).
    void Reset(int frames_per_buffer);

    // Pushes all audio channel data from |input_bus| through the FIFO.  This will
    // result in zero, one, or multiple synchronous calls to the OutputCallback
    // provided in the constructor.  If the |input_bus| has a different number of
    // channels than the prior Push() call, any currently-queued frames will be
    // dropped.
    void Push(const AudioBus& input_bus);

    // Flushes any enqueued frames by invoking the OutputCallback with those
    // frames plus padded zero samples.  If there are no frames currently
    // enqueued, OutputCallback is not run.
    void Flush();

private:
    const OutputCallback callback_;

    int frames_per_buffer_;

    // Queue of frames pending for delivery.
    std::unique_ptr<AudioBus> audio_queue_;
    int queued_frames_;

    DISALLOW_COPY_AND_ASSIGN(AudioPushFifo);
};

} // namespace media

#endif // MEDIA_BASE_AUDIO_PUSH_FIFO_H_
